Prostacyclin synthesis is reduced in human atherosclerotic disease, in animal models of atherosclerosis, and in subcultured populations of aortic smooth muscle cells derived from atherosclerotic aorta. However, the mechanism of reduced prostacyclin synthesis by atherosclerotic tissue is unknown. The objectives of experiments proposed in Specific Aim One are: (i) to determine if prostanoid production is reduced in aortic smooth muscle cells grown in tissue culture that have accumulated both free and esterified cholesterol by exposure to cationized LDL; and (ii) to investigate potential mechanisms by which prostanoid production is reduced by cholesterol-enriched cells. Such mechanisms that will be studied include: (a) reduction in uptake and distribution of arachidonate in cellular phospholipids; (b) direct inhibition of phospholipases A2 and C; (c) inhibition of cyclooxygenase; (d) inhibition of prostacyclin synthetase; and (e) competitive inhibition of conversion of arachidonate to cyclooxygenase products by linoleate derived from LDL. Plasma high density lipoproteins promote net cellular cholesterol efflux from vascular smooth muscle cells. Plasma high density lipoproteins also stimulate prostacyclin and PGE2 synthesis by aortic smooth muscle cells by providing arachidonate as substrate. Prostacyclin may promote net cellular cholesterol efflux by increasing the activities of acid and neutral cholesterol ester hydrolases, while PGE2 may promote net cholesterol efflux by inhibition the activity of Acyl-CoA-cholesterol acyltransferase. These data suggest that one potential mechanism of HDL-induced cholesterol efflux may be its ability to stimulate smooth muscle cell PGI2 and PGE2 synthesis. The objectives of experiments proposed in Specific Aim Two are: (i) to determine if HDL-induced cholesterol efflux is dependent upon HDL-induced prostanoid synthesis; and (ii) to determine if the mechanism of HDL-induced cholesterol efflux is in part due to eicosanoid-mediated alterations in Acyl-CoA cholesterol acyltransferase and neutral cholesteryl ester hydrolase in both normal and cholesterol-enriched cells. Results from these experiments will contribute to our understanding of the possible influence of HDL-induced eicosanoid synthesis on HDL-induced cholesterol efflux.